1. Field of the Invention
The present invention relates to a pulse radar device that detects presence or absence of an object and measures a distance to the detected object by transmitting a radio wave and receiving a reflection wave generated by the reflection of the transmitted radio wave by the object.
2. Description of the Related Art
A conventional pulse radar device will be described with reference to the drawings. FIG. 21 shows the construction of a conventional pulse radar device that is, for instance, disclosed in Japanese Patent Laid-Open No. 07-072237.
As shown in FIG. 21, this pulse radar device periodically outputs a pulse-shaped signal using a pulse signal sending means 901. Then, the pulse radar device continuously receives a reflection pulse from an object using a reflection pulse signal receiving means 903 and converts the reflection pulse into a binary signal using a binarization means (not shown) Then, after a sending timing of the sending means 901, a sampling means 904 obtains a sampling value of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d by sampling the binary signal at one fixed sampling point or at each of plural sampling points and gives this sampling value to an adding and storing means 905 corresponding to each sampling point.
On receiving the sampling value, the adding and storing means 905 adds the sampling value of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d in accordance with a predetermined number of times of signal sending by the sending means 901. After the addition is performed a predetermined number of times, a judging means 906 divides a value obtained as a result of addition by each adding and storing means 905 by the number of times of addition to obtain a normalized addition value, compares the normalized addition value with a predetermined threshold value, judges whether there exists a reflection signal from an external object based on the magnitude of the normalized addition value, and judges the presence or absence of the external object based on a result of this judgment.
However, in the case where the isolation between the transmission and the reception is low such that there exists a so-called leakage waveform, or in the case where there exists a radome, it becomes difficult to detect an object, which is less than 10 m away, and to measure a distance to the object using the device described above due to the reasons given below.
That is, in the conventional device described above, its transmission pulse width is 66.7 ns corresponding to a distance of 10 m. Consequently, in the case where an object is less than 10 m away, there is detected a waveform in which a leakage waveform or a waveform in which the waveform of a reflection wave generated by a secondary radome is superimposed on the waveform of a reflection wave from the object, as shown in FIGS. 22A to 22D. As a result, if a threshold value is set based on a reception level during non-transmission, that is, based on a so-called noise level, there is detected only the rising of the leakage waveform and there occurs a problem in that it is impossible to detect the rising of the reflection wave that should be actually detected.
As a measure against such a problem, a method, with which a pulse width is extremely reduced to 350 ps or the like, is proposed in a document of 1998 (W. Weidmann and D. Steinbuch, xe2x80x9cHigh Resolution Radar for Short Range Automotive Applicationsxe2x80x9d, 28th European Microwave Conference Amsterdam, 1998). There is also proposed a method, with which a leakage waveform is canceled out by utilizing a transmission waveform, in JP 10-62518 A.
If the transmission pulse width is reduced to 350 ps as described in the document described above, the aforementioned problem is solved because a leakage waveform and the waveform of a reflection wave are superimposed on each other only in the case where the distance to an object is around 5 cm or shorter. However, its occupation band width is extremely widened, so that there occurs a problem in that it is impossible to use this method within the limits of the existing radio law.
Also, in the case where a leakage waveform is canceled out by utilizing a transmission waveform with the method described in Japanese Patent Laid-Open No. 10-062518, it is difficult to cope with a difference in time intervals from transmission to the reception of a leakage waveform resulting from an individual difference or a difference of the use condition, a difference in the magnitude of the leakage waveform, and the like. This results in a problem in that it is required to perform adjustment in accordance with the circumstances.
The present invention has been made to solve the problems described above, and an object of the present invention is to provide a pulse radar device that is capable of correctly detecting an object within limits of existing radio law even if there exists a leakage signal between transmission and reception or there exists a reflection signal from a target, such as radome, fixed onto the pulse radar device. To do so, the pulse radar device utilizes a fact that a reception signal is changed if a phase difference between a leakage signal between transmission and reception and a reflection signal from a moving target is changed or a phase difference between a reflection signal from a target, such as radome, fixed onto the radar device and a reflection signal from a moving target is changed, as shown in FIG. 1.
According to the present invention, there is provided a pulse radar device including a transmitting means for transmitting a pulse-shaped radio wave and a receiving means for receiving a reflection wave generated by reflection of the radio wave transmitted from the transmitting means by an object.
The pulse radar device according to the present invention further includes a comparator means for converting a reception signal from the receiving means into a binary signal by comparing the reception signal with a preset and predetermined level and a first integrating means for sampling an output from the comparator means at predetermined time intervals from transmission and integrating results of a predetermined number of times of the sampling at each sampling timing.
The pulse radar device according to the present invention further includes a differential operating means for, each time a predetermined time period has passed, reading results of the integrating by the first integrating means at each sampling timing and differentiating the read results of the integrating in a sampling direction and a second integrating means for integrating absolute values of a predetermined number of outputs from the differential operating means at each sampling timing.
The pulse radar device according to the present invention still further includes a peak detecting means for detecting a peak based on an output from the second integrating means, a distance measuring and detecting means for calculating a distance to the object and judging presence or absence of the object based on an output from the peak detecting means and a timing control means for performing timing control for the transmission of the radio wave, the reception of the reflection wave, and signal processing.
Therefore, the pulse radar device according to the present invention is capable of correctly detecting an object even if there exists a so-called leakage signal component.